File:The cell in development and inheritance (1902) (14596667477).jpg

Identifier: cellindevelopmenwils2 (find matches)
Title: The cell in development and inheritance
Year: 1902 (1900s)
Authors: Wilson, Edmund B. (Edmund Beecher), 1856-1939
Subjects: Cell Physiological Phenomena Cells
Publisher: New York : Macmillan
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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to the physi-ological meaning of a process so general and one that has been thesubject of such prolonged research. Both the foregoing general viewsare in harmony with the results of Darwins work on variation andwith the experience of practical breeders, which have shown that ^ Cf. Joukowsky, 99. ^ Amphimixis, 1S91. 2 The Law of Heredity, 18S3. * 99, p. 326. i8o FERTILIZATION OF THE OVUM crossing produces both greater vigour and greater variability. In viewof all the facts, however, we are constrained to the admission that theessential nature of sexual reproduction must remain undetermined untilthe subject shall have been far more thoroughly investigated, espe-cially in the unicellular forms, where the key to the ultimate problemis undoubtedly to be sought. A. Preliminary General Sketch Among the unicellular plants and animals, fertilization is effectedby means of conjugation, a process in which two individuals eitherfuse together permanently or unite temporarily and effect an exchange
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Fig. 89. — Fertilization of the egg of the snail, Physa. (Kostanecki and Wierzejski.)A. The entire spermatozoon lies in the egg, its nucleus at the right, fiagellum at the left, whilethe minute sperm-amphiaster occupies the position of the middle-piece. The first polar body hasbeen formed, the second is forming. B. The enlarged sperm-nucleus and sperm-amphiaster lienear the centre; second polar body forming and the first dividing. The egg-centrosomes andasters afterward disappear, their place being taken by those of the spermatozoon. of nuclear matter, after which they separate. In all the Jiigher formsfertilisation consists in the permanent fusion of tzvo germ-cells, one ofpaterjial and one of maternal origin. We may first consider the fer-tilization of the animal Q.%g, which appears to take place in essentiallythe same manner throughout the animal kingdom, and to be closelyparalleled by the corresponding process in plants. PRELIMINARY GENERAL SKETCH l8l Leeuwenhoek, whose pupil Ha

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